The British billionaire Joe Lewis splashed out millions of dollars on Bear Stearns shares just a few hours before the troubled investment bank ran out of money last week and appealed to the Federal Reserve for a bail-out.

A filing at the US securities and exchange commission by Lewis's Florida-based Tavistock investment company reveals that the London-born entre-preneur increased his stake in Bear Stearns on Thursday last week by buying 569,000 shares at $55.13, for a total cost of $31m (£15.6m). His investment went sour spectacularly quickly. The Wall Street firm faced a run on the bank that afternoon and began looking for an emergency cash injection in the evening. By Sunday, it had agreed a fire sale to JP Morgan for $2 a share.

Lewis, who lives in the Bahamas, has said little publicly other than to describe JP Morgan's takeover as "derisory". His spokesman did not return calls. But Tavistock's SEC filing lays down the lines of battle with Bear Stearns by warning that he was likely to fight the deal.

"The reporting persons are evaluating recent events and the proposed transaction and will take whatever action that they deem necessary and appropriate to protect the value of their investment in the shares," said the document.

It adds that Lewis and his colleagues may "attempt to encourage the issuer [Bear Stearns] and third parties to consider other strategic transactions or alternatives".

Lewis's total stake in Bear Stearns is 8.35% and his total losses on the bank's collapse are thought to be more than $1bn - almost half of the currency dealer's estimated $2.5bn fortune. He appears to have remained bullish on the stock to the bitter end - his SEC filing reveals that he spent $38m on two large chunks of equity during February at share prices of $86 and $79. There were suggestions yesterday that the SEC is investigating suspicious movements in Bear Stearns options in the run-up to the institution's demise.

The Wall Street Journal reported that the regulator, which declined to comment, is particularly interested in a surge in "put" options, which allow investors to bet on a decline in the share price. While the share price was hovering at $50, speculators were seeking options contracts to sell at as little as $20.

Anxious to avoid an exodus of talent, JP Morgan is offering bonuses in both cash and shares to Bear Stearns bankers who agree to stay on under the firm's new ownership.

At a tense 45-minute meeting with several hundred Bear Stearns executives, JP Morgan's boss, Jamie Dimon, expressed sympathy for the financial "tsunami" that destabilised the firm, although he replied with a straightforward "no" when asked whether he would raise the takeover price.

Dimon got a rough reception. Witnesses told the New York Times that one Bear executive told him: "I think it's galling you come into our house and you call this a 'merger'."

Many Bear Stearns staff resent the fact that JP Morgan executives have already installed themselves in conference rooms and are in effect running the investment bank despite the fact that the rescue takeover has yet to win approval from shareholders.

Dimon told the troubled bank's employees that his heart went out to them: "I feel terrible sometimes when people think we took advantage. I don't think we could possibly know what you all are feeling, but I hope that you give JP Morgan a chance."